1. Technical Field
The present invention pertains to improvements in ultra-wide bandwidth baluns for dish antennas. In particular, the invention is an improvement of the apparatus disclosed in U.S. Pat. No. 5,379,006 (McCorkle). The disclosure in the patent is expressly incorporated by reference herein in its entirety.
2. Discussion of Prior Art
Impulse radar has numerous uses in various radar systems to detect aircraft, ground vehicles, people, mines, buried pipes, roadways, etc. Transmitting antennas for these systems typically require a balanced feed, while transmitters typically produce energy in an unbalanced feed. Numerous commercially available baluns do not have the bandwidth, balance, insertion loss or power handling capabilities required for ultra-wide bandwidth (UWB) applications, that is, applications involving frequencies from DC to gigahertz (GHz).
The above-referenced McCorkle U.S. Pat. No. (5,379,006) discloses in FIG. 4 of that patent a balun for ultra-wide bandwidth applications. Specifically, an input transmission line is connected in parallel with two output transmission lines such that one output transmission line is inverted with respect to the other. Each of the two output transmission lines has twice the characteristic impedance of the input transmission line, and all three of the transmission lines have a center conductor surrounded by an exterior shield (e.g., coaxial lines). At a junction where the input transmission line is connected in parallel with the two output transmission lines, the center conductor of the input transmission line is connected to coupled exterior shields of the two output transmission lines. Each of the center conductors of the two output transmission lines are connected to the exterior shield of the input transmission line. This configuration enables a signal from the input transmission line to be divided into two equal and opposite signals, each to be carried by a corresponding one of the two transmission lines. Ferrite cores along each of the two transmission lines provide inductance to isolate the parallel connection of the transmission lines and form balanced signals. For matching over the range of UWB frequencies (i.e., DC to GHz), an RC network is placed between exterior shields of the two transmission lines subsequent to the parallel connection. This balun has the capability of ultra-wide bandwidth applications from DC to GHz.
While the above-described balun provides a balanced feed, it would be desirable to mount the balun in a manner that avoids obstructing the antenna aperture. Further, it would be desirable to feed dish antennas through the feed arms of the antenna.